1. Field of the Invention
This invention relates to a process for reclaiming and recycling a noble metal catalyst used in the reaction of an aromatic nitro compound or aromatic amine in the presence of an oxidation agent, with a hydroxyl compound and carbon monoxide to manufacture an aromatic urethane. The noble metal catalyst is treated with hydrogen upon completion of urethane formation in the reaction solution. The precipitated noble metal is separated and, together with a hydrohalic acid, is reused as a catalyst.
2. Description of the Prior Art
The manufacture of aromatic urethanes by reaction of aromatic nitro compounds, hydroxyl group containing organic compounds and carbon monoxide in the presence of catalysts is described in German Published Application 1,568,044 (U.S. Pat. No. 3,467,694), German Published Application 2,555,557 (Great Britain Pat. No. 1,469,222), German Application 2,603,574 (Great Britain Pat. No. 1,472,243) and European Published Application, 0,000,563.
According to data in German Patent Application P 29 10 132.4, aromatic urethanes are obtained by reacting aromatic amines with hydroxyl compounds, carbon monoxide and an oxygen and/or nitrogen compound as an oxidation agent at increased pressure in the presence of catalysts.
Catalysts for both of the above processes are noble metals such as platinum, paladium, ruthenium, rhodium, osmium and iridium and chemical compounds of these noble metals, for instance, their oxides, sulfates, nitrates, halides, acetates and others. Their noble metal catalysts are preferably used together with co-catalysts such as Lewis acids, nitrogen-containing heterocyclical compounds, iron, copper or tin halides, and tertiary amines, Lewis acids and organic primary amines, ureas, biurets, allophanates or their mixtures, tin, titanium, iron, mercury, nickle, vanadium, antimony, manganese, cobalt, and/or copper compounds. Under these conditions, the noble metal catalysts are dissolved in part during the reaction so that they cannot be reclaimed from the reaction solution by simple mechanical separating methods such as decanting or filtering. If elementary, palladium deposited onto a carrier is used as catalyst, the analysis of the reaction discharge separated from the residue shows that considerable quantities of palladium are dissolved and thus discharged using this method also. Therefore, considerable losses of noble metals must be accepted for all cases which render these processes, particularly their large-scale implementation, expensive and non-economical.
A purpose of this invention was to reduce the loss of noble metal catalysts used for the processes for the manufacture of aromatic urethanes from aromatic nitro compounds or aromatic amines in the presence of an oxidant, hydroxyl compounds and carbon monoxide so that the processes become profitable and a once used noble metal catalyst can be reused for a large number of reaction cycles.